Vacuum tube and method of treating thereof



y 1932- NACHUMSOHN 1,359,679

VACUUM TUBE AND METHOD OF TREATING THEREOF Filed March 28, 1928 Patented May 24, 1932 UNITED STATES IRVING NACHUMSOHN, OF CHICAGO, ILLINOIS VACUUM TUBE AND METHOD OF TREATING THEREOF Application filed March 28,1928. ,Serial No. 265,391.

My invention relates to improvements in vacuum tubes and the like, and method of treating thereof; one of its objects being to improve, simplify and reduce the cost of manufacture thereof by applying the heat directly to the desired area, thereby obviating the unnecessary overheating of the parts.

To the attainment of these ends and the accomplishment of other new and useful objects as will appear, the invention consists in the features of novelty in substantially the construction, combination and arrangement of parts hereinafter described and claimed and shown in the accompanying drawing, in which there is shown a schematic diagram illustrating a method by means of which this invention may be carried out.

In the drawing, Fig. 1, the numeral 2 designates the filament wire, 3 an equipotential cathode through which the filament wire passes, 4 the grid, 5 the plate and 6 the vessel which encloses the elements and which is exhausted through exhaust tube 7 Connected also with cathode 3 are conductors 8 and 9, having external connections,

and through which conductors a current is passed to heat the cathode. A portion of these conductors, as at 10 of conductor 8, is of such cross section that the maximum capacity of current which it will carry will be less than the capacity of the rest of the circuit of which it forms a part during the treating process and for a purpose to be set forth.

In order to make the cathode 3 emit electrons at a comparatively low temperature it is coated with certain chemicals, well known in the art, such as barium carbonate, and in order to render the coating suitable for use it must be properly formed and treated by the application of heat.

,VVhen the heat is applied the chemicals are then treated to cause them to be converted into a condition that when in use in the tube they will facilitate the emission of electrons to the plate 5.

In common practice, during the process of manufacturing this type of equipote-ntial cathode tube, it is customary to heat the cathode indirectly by different means. For example, in some instances the cathode and the coating thereon are heated to the required temperature by the application of sufiicient current to'the filament wire. This temperature is usually greater than the normal operating temperature of the filament and the '1 heat will pass through to the cathode, heating the latter sufliciently to treat the coating thereon.

Another method has beento apply the necessary heat inductively, by placing the tube while it is being exhaustedwithin a high frequency coil, thus heating all the elements of the tube,includingthe cathode, by means of a high frequency current. a

In other instances these methods have been "5 combined. In any of the prior methods the cathode is thus heated, for the purpose of forming the coating and liberating detrimental gases fromthe metallic parts, as well as from the coating. One of the main objections to the prior methods'is that the heat is not concentrated at the area where'it ismost beneficial, with the result that some of the parts will be unnecessarily overheated, and. the cost of manufacture is expensive and wasteful.

One of the objects of the present invention is to apply the heat, during the manufacture of the tube, directly to the element or part which requires it.

It is to be clearly understood that this invention does not apply to such types of tubes in which the filament itself is used as a cathode, or where there is during normal op eration of the tube a potential gradient T along the length of the cathode due to the current used for heating purposes. It does, however, apply to such types of tubes known as equipotential or heater types.

In carrying this invention into operation the cathode 3 may be heated by means of a current from any suitable source, such as from the winding 3 of a transformer T. During the pumping operation it is also sometimes desirable to bombard the plate 5 with electrons and for this purpose the transformer may be provided with an additional plate-voltage winding 5'.

After the cathode has thus been sufficiently treated, and it is desired to electrically dispense with one of the conductors leading to the cathode, this may be accomplished in any suitable manner, such for instance as providing in one of the conductors a portion 10 having a property adapted to be electrically destroyed or fused Without causing injury to any of the other portions of the circuit.

This may be accomplished by raising the voltage until an excessive current flows through the circuit 3'10839, causing fusion of a predetermined portion, such as 10, heretofore described.

In ordinary devices of the class described the gaseous pressure Within the vessel is very .low and, therefore, only a small amount of the internal heat is conducted directly to the Walls of the vessel, due to the thermal resistivity of the vacuous insulation. The efficiency of the cathode heating element therefore depends, to a remarkable degree, upon the amount of heat conducted externally of the vessel through the leads. Since in the ultimate use of the device herein illustrated only one lead Wire is required for the cathode, I prefer to disconnect one of the other Wires, as conductor 8, after it is no longer required for treating purposes.

Having now particularly described the nature of this invention and the manner in which the same may be performed, I declare that What I claim as new is In the manufacture of vacuum tubes havinga filament Wire and an equipotential cathode disposed therearound, means for conducting a current through the cathode for heat treating said cathode, the said means embodying lead Wires attached to the longitudinally opposed ends of said cathode, one of saidlead Wires being more easily fusible than the other of said wires.

IRVING NAGHUMSOHN. 

